Electric discharge device



Nov. 10, 1936. v. J. FRANCIS ET AL 2,060,564

ELECTRIC DISCHARGE DEVICE Filed on. 15, 1935 Q o E I ATTORNEY Patented Nov. 10, 1936 UNITED STATES ELECTRIC DISCHARGE DEVICE Victor James Francis, North Wembley, andJohn Walter Ryde, London, England, assignors to General Electric Company, a corporation of New York Application October 15, 1935, Serial No. 45,160 In Great Britain October 11, 1934 2 Claims. (Cl. 176-2) This invention relates to electric discharge devices of the high-pressure metal-vapour type having an inner. tube through which the discharge passes and an outer envelope enclosing it.

5 i In British patent specification No. 431,651 which corresponds to the United States Patent Number 2,030,437 we have described how the introduction of suitable gases into the space betweeen the tube and the envelope reduces the blackening of the inner tube during life. We

have now found that, in some cases, the introduction of oxygen, or of gases containing oxygen, reduces blackening even if the gas is subsequently removed and remains absent during the main Dart of the life.

Thus, in the manufacture of a high-pressure mercury vapour discharge lamp of normal type,

if oxygen at a pressure of millimetres is introduced into the envelope, if the lamp is then 20 run under normal operating conditions for an hour, and if the oxygen is then pumped out and the evacuated envelope sealed off, then the blackening of such a lamp during life may be very much less than that of a lamp whose envelope was evacuated before the first operation.

Hydrogen, which is approximately as efiicient as oxygen in preventing blackening, if left in the envelope, cannot be substituted for oxygen in this process. If hydrogen, introduced into the envelope, is subsequently pumped out, blackening proceeds from the time of pumping out almost or quite as ifthe hydrogen had never been introduced.

Some at least of the effect due to operating the lamp with the gas in the space arises from the heating of the inner tube which accompanies such operation.' For if, while there is oxygen in the envelope, the tube, instead of having a current passed through it issimpiy baked-in an' 40 oven to the temperature which it reaches in operation and maintained at that temperature for the same period, some at least of the beneficial eflect of the oxygen is obtained. Owing to the unavoidable irregularity in all measurements of rate of blackening, it is dimcult to be sure whether the full effect is obtained by baking without the passage of a current.

Further it is not essential that the outer envelope should be present during the treatment (1. e. operation or baking) of the inner tube. The effect can be obtained by treating the inner tube, devoid of its outer envelope, in atmospheric air or in oxygen contained in a subsidiary vessel and then sealing it into its outer envelope. More will be said on this matter below.

According to the invention the manufacture of an electric discharge device of the type specified comprises the steps of operating and/or baking the device for a substantial period while the inner tube is surrounded by suitable oxygen- 5 containing gas, and of subsequently removing the said gas, so that the device is operatedfor its normal life without any substantial amount of oxygen-containing gas between the inner tube and outer envelope. 10

The extent of the beneficial effect obtained by the treatment of the inner tube for a given period increases with the pressure of the surroundirig oxygen-containing gas. Thus, for the same period of the same treatment, more effect is ob- 15 tained by treating in oxygen at mm. pressure than in oxygen at 10 mm. pressure. There appears to be no upper limit to the permissible pressure; but there are practical inconveniences, evident to those skilled in the art, in the use of 20 pressure much higher than 100 mm.

Pure oxygen is more effective than air containing the same concentration of oxygen. There appears to be no reason why any gas but air or oxygen should be used in practice; but of 25 course other mixtures of oxygen with-neutral gases might be used. Noevidence has been obtained that gases in which oxygen is present in chemical combination are effective, and the words oxygen-containing. must be interpreted 30 to mean containing free oxygen. But if a gas could be found which, though not'originally containing free oxygen, developed free oxygen in contact with the heated inner tube, such a gas would be oxygen-containing for the purpose of the invention. Throughout this specification, gas means matter in the gaseous state whether it is above or below its critical temperature.

- It is in general desirable that the treatment should be as severe as the glass of the inner tube permits; that is to say, if treatment is by the passage of a discharge, the full operating current should be passed, and if it is by baking, the temperature should be as high as that attained in full operation. But some beneficial 5 effect can be obtained by less severe treatments. It is to be observed that the period of treatment cannot be prolonged indefinitely, even in principle; for the period must obviously be short especially liable to occur if the treatment has been light, that is to say, if the gas pressure has been low and/or the temperature low and/or the time short. If the treatment has been severe, the inner tubes can be subjected to,ordinary handling without danger; indeed in order to remove the efiect of the treatment it may be necessary to apply some special process, such as acid washing. Accordingly if the inner tube is tobe sealed into the outer envelope after treat-. ment, it is desirable that the treatment should not be very light.

The glass used in experiments on which the foregoing statements are based had roughly the composition given in the table of the 'above mentioned specification. It is possible again that the statements might have required some modification if other glasses had been used.

We claim:

1. The method of retarding the discoloration of the discharge space defining surface of an electric discharge device having a sealed inhandling of the tube after treatment. This is nertube through which the discharge passes and a sealed outer envelope enclosing said tube, which method comprises the steps of introducing a suitable oxygen containing gas at a pressure between 10 and 100 mm. of mercury around the said sealed inner tube, heating said tube for a. substantial period in the presence of said gas and then removing the said gas.

2. The method of retarding the discoloration of the dischargespace defining surface of an electric discharge device having an inner sealed tube through which the discharge passes and a sealed outer envelope enclosing said tube, which method comprises the steps of surrounding the said sealed inner tube with a suitable oxygen containing gas at a pressure between 10 and 100 mm. of mercury, heating said inner tube in the presence of said gas, mounting said inner tube in an outer envelope and then removing the said gas. VIGIOR JAMES FRANCIS JOHN WALTER RYDE. 

